1. Field of the Invention
The present invention relates to transmission power control of a user equipment apparatus, and more particularly to, transmission power control of a user equipment apparatus for simultaneously transmitting signals from a plurality of wireless communication chips to which different wireless communication schemes are applied.
2. Discussion of the Related Art
With breakthrough of the wireless communication technology, demand on the electric wave increases, and the electric wave is widely used in the field of medical service and traffic, and daily life as well as the field of communication and broadcasting. With the increase of electronic and electric devices, the electromagnetic wave radiated from electric wave facilities and devices has greatly affected a human body. In particular, federal communication commission (FCC) of the US has adopted guidelines on environmental impact assessment of radio frequency radiation of FCC 96-326 to prescribe a limit of local power absorption, which will be applied to a random portable transmitting device.
The limit of maximum allowable exposure prescribed in the guidelines is based on exposure assessment criterion quantified by a specific absorption rate (SAR) rule that is the standard of a radio frequency (RF) energy absorption rate. If the electromagnetic wave is radiated towards a human body, quantitative assessment on the electromagnetic wave is performed by SAR measurement through animal test, power measurement and analysis of electromagnetic fields, wherein the SAR is represented by absorption power per unit mass, which is absorbed in the human body by exposure of the human body to the electromagnetic fields.
In addition to the FCC of the US, CENELEC of the Europe has prescribed the SAR condition as requirements of conformity assessment of a mobile communication terminal. Although there is the difference in reference values of the electromagnetic wave SAR rule, the FCC of the US and the CENELEC of the Europe prescribe the SAR condition as an important guideline of conformity assessment of the mobile communication terminal. Accordingly, the mobile communication terminal should satisfy the SAR condition (or rule).
The most general method for satisfying the SAR value is that the mobile communication terminal is located far away from the human body if possible. If signals should be transmitted simultaneously through a plurality of frequency bands as suggested in the present invention, it is general that two antennas are used. In this case, the SAR value may not satisfy the prescribed value due to restriction of the location of the antennas.
Accordingly, if the antennas are located at a place the farthest away from the human body and RF front end is designed to simultaneously transmit signals to one antenna through a plurality of frequency bands, the most optimized SAR value can be obtained. Hereinafter, a solution for satisfying the SAR condition and solving the problem of intermodulation distortion (IMD) will be described. In this specification, band 2, band 5 and band 13 correspond to different frequency bands.
The limit of maximum allowable exposure prescribed in the guidelines is based on exposure assessment criterion quantified by a specific absorption rate (SAR) rule that is the standard of a radio frequency (RF) energy absorption rate. If the electromagnetic wave is radiated towards a human body, quantitative assessment on the electromagnetic wave is performed by SAR measurement through animal test, power measurement and analysis of electromagnetic fields, wherein the SAR is represented by absorption power per unit mass, which is absorbed in the human body by exposure of the human body to the electromagnetic fields.
In addition to the FCC of the US, CENELEC of the Europe has prescribed the SAR condition as requirements of conformity assessment of a mobile communication terminal. Although there is the difference in reference values of the electromagnetic wave SAR rule, the FCC of the US or the CENELEC of the Europe prescribe the SAR condition as an important guideline of conformity assessment of the mobile communication terminal. Accordingly, the mobile communication terminal should satisfy the SAR condition (or rule).
Generally, in a wireless communication system, a user equipment should follow the SAR rule even if it simultaneously transmits signals through two or more frequency bands. In other words, if the user equipment simultaneously transmits signals from a plurality of wireless communication chips to which different wireless communication schemes are applied, it may exceed the SAR standard. In addition to the problem of the SAR standard, interference occurs between the signals, which are simultaneously transmitted, due to intermodulation distortion (IMD) (also referred to as IM3). For this reason, a problem occurs in that communication throughput is remarkably deteriorated.
However, detailed solutions for the problems of the SAR standard and the IMD have not been suggested until now.